There is a fundamental gap between the discovery of proven-effective intensive care unit (ICU) sedation, mechanical ventilation, mobility, and symptom management strategies and approaches that can equip ICU providers with the skills necessary to reliably adopt these interventions in everyday practice. Until this gap is filled, the millions of patients with heart, lung, and blood disorders admitted to ICUs annually will remain at risk for avoidable physical, mental, and cognitive health impairments that may persist for months to years after hospital discharge. In the proposed study, we will continue our partnership with the Society of Critical Care Medicine's (SCCM's) ICU Liberation Collaborative; a national quality improvement network comprised of 68 academic, community, and federal ICUs. Guided by the Consolidated Framework for Implementation Research, the overall objective of the Determinants of Implementation Success Coordinating Ventilator, Early Ambulation and Rehabilitation Efforts in the ICU (DISCOVER-ICU) study is to develop multilevel implementation strategies to enhance sustainable adoption of the ABCDEF bundle in routine ICU practice. The ABCDEF bundle is an evidence-based, multicomponent ICU management strategy that incorporates many of the SCCM's Clinical Practice Guidelines for the Management of Pain, Agitation, and Delirium in Adult Patients in the ICU. Using a multiphase, sequential, mixed-methods design, this study has three specific aims: 1) estimate the effects of patient-level characteristics on ABCDEF bundle adoption; 2) examine unit-level variation in ABCDEF bundle adoption and associated provider- and organization-level characteristics; and 3) determine which implementation strategies result in the greatest adoption of the ABCDEF bundle. We will use existing deidentified data obtained from >15,000 patients, >5,000 interprofessional ICU team members, and 68 hospitals participating in the ICU Liberation Collaborative to achieve specific aims 1 and 2. For specific aim 3, we will extend data collection using interprofessional ICU team surveys, a modified Delphi process, and concept mapping to achieve greater understanding of implementation strategies that prove most effective for ABCDEF bundle adoption. Our focus on high- and low-ABCDEF bundle-performing units will allow us to select and tailor potential ABCDEF bundle implementation strategies to meet specific local contextual needs. This approach in innovative because it: capitalizes on existing data from a large, nationally representative network of ICUs; includes units with already known and highly variable ABCDEF bundle performance rates and implementation strategies; and allows for the examination of actual versus perceived ABCDEF Bundle performance. Results of this work will directly lead to the development of implementation strategies that are adaptable, responsive to community needs, and account for the cultural and organizational factors necessary to increase ABCDEF bundle adoption. These implementation strategies will then be tested in a future cluster randomized hybrid II implementation- effectiveness trial.